Analysis of a Streptococcus pyogenes Puerperal Sepsis Cluster by Use of Whole-Genome Sequencing

TLDR: Traditional typing protocols, such as pulsed-field gel electrophoresis, may not be sensitive enough to allow fine epidemiological discrimination of closely related bacterial isolates, and whole-genome sequencing presents a valid alternative that allows accurate fine-scale epidemiological investigation of bacterial infectious disease.

Abstract: Between June and November 2010, a concerning rise in the number of cases of puerperal sepsis, a postpartum pelvic bacterial infection contracted by women after childbirth, was observed in the New South Wales, Australia, hospital system Group A streptococcus (GAS; Streptococcus pyogenes) isolates PS001 to PS011 were recovered from nine patients Pulsed-field gel electrophoresis and emm sequence typing revealed that GAS of emm140, emm750, emm770, emm890, and emm899 were each recovered from a single patient, ruling out a single source of infection However, emm288 GAS were recovered from four different patients To investigate the relatedness of these emm28 isolates, whole-genome sequencing was undertaken and the genome sequences were compared to the genome sequence of the emm284 reference strain, MGAS6180 A total of 186 single nucleotide polymorphisms were identified, for which the phylogenetic reconstruction indicated an outbreak of a polyclonal nature While two isolates collected from different hospitals were not closely related, isolates from two puerperal sepsis patients from the same hospital were indistinguishable, suggesting patient-to-patient transmission or infection from a common source The results of this study indicate that traditional typing protocols, such as pulsed-field gel electrophoresis, may not be sensitive enough to allow fine epidemiological discrimination of closely related bacterial isolates Whole-genome sequencing presents a valid alternative that allows accurate fine-scale epidemiological investigation of bacterial infectious disease